180
R. LALLIER
(ascorbigen) or in a free form. The bound form quickly disappears during
cleavage. The free ascorbic acid content presents a series of
fluctuations
during the blastula stages and during gastrulation, but afterwards
increases. This increase depends mainly on a new accumulation of
ascorbigen.
In the vegetalized larvae, the ascorbic acid content is somewhat lower
than in the controls before hatching. After hatching the bound ascorbic
acid quickly increases and rises above the level of the controls.
In the animalized larvae, the ascorbic acid content decreases for the
first few hours, then increases and attains higher values than the
controls during late blastula stages and at hatching. After hatching, no
ascorbigen is accumulated in the animalized larvae and the ascorbic acid
content slowly decreases. These observations show that the bound
ascorbic acid accumulates during the differentiation of the entomesoderm.
The study of the distribution of ascorbic acid by Eränkö's silver
impregnation method confirms the relationship observed between the
accumulation of ascorbic acid and the development of the entomesoderm
(Bäckström, 1957). The morphogenetic effects of ascorbic acid and its
antimetabolite, glucoascorbic acid, also reinforce the idea that the
accumulation of ascorbic acid is connected with entomesodermal
differentiation. Indeed, ascorbic acid increases the vegetalizing effect of
lithium (Runnström, 1956), whereas glucoascorbic acid promotes the
animalization of isolated animal halves (Gustafson and Hörstadius,
1955). Does ascorbic acid intervene in the formation of the reduction
gradients? In sea urchin eggs, at all stages, ascorbic acid practically
exists only in a reduced form. In later gastrula stages, ascorbic acid is
distributed in a vegetal-animal gradient. At the blastula stage, when the
first gradient of reduction in an animal-vegetal direction is formed, the
ascorbic acid seems regularly distributed. At this stage no connection
appears to exist between ascorbic acid distribution and the animalvegetal reduction gradient.
The SH-containing substances constitute another group of reducing
substances. They have been studied by Bäckström (1958b, 1959a) by
histochemical and biochemical methods. —SH groups have been determined in the protein fractions and the soluble non-protein fractions.
The non-protein fraction seems essentially made up of glutathione.
During the cleavage and gastrula stages the content of —SH groups
shows cyclical changes. In embryos treated by lithium, as well as in
embryos animalized by iodosobenzoic acid, the —SH content is lower
than that in the controls. At hatching the normal, animalized or
vegetalized larvae have the same —SH content. After hatching the —SH
content decreases in the three types of larva. The decrease is faster in
the vegetalized larva, and slower in the animalized larva than in the
R. LALLIER
(ascorbigen) or in a free form. The bound form quickly disappears during
cleavage. The free ascorbic acid content presents a series of
fluctuations
during the blastula stages and during gastrulation, but afterwards
increases. This increase depends mainly on a new accumulation of
ascorbigen.
In the vegetalized larvae, the ascorbic acid content is somewhat lower
than in the controls before hatching. After hatching the bound ascorbic
acid quickly increases and rises above the level of the controls.
In the animalized larvae, the ascorbic acid content decreases for the
first few hours, then increases and attains higher values than the
controls during late blastula stages and at hatching. After hatching, no
ascorbigen is accumulated in the animalized larvae and the ascorbic acid
content slowly decreases. These observations show that the bound
ascorbic acid accumulates during the differentiation of the entomesoderm.
The study of the distribution of ascorbic acid by Eränkö's silver
impregnation method confirms the relationship observed between the
accumulation of ascorbic acid and the development of the entomesoderm
(Bäckström, 1957). The morphogenetic effects of ascorbic acid and its
antimetabolite, glucoascorbic acid, also reinforce the idea that the
accumulation of ascorbic acid is connected with entomesodermal
differentiation. Indeed, ascorbic acid increases the vegetalizing effect of
lithium (Runnström, 1956), whereas glucoascorbic acid promotes the
animalization of isolated animal halves (Gustafson and Hörstadius,
1955). Does ascorbic acid intervene in the formation of the reduction
gradients? In sea urchin eggs, at all stages, ascorbic acid practically
exists only in a reduced form. In later gastrula stages, ascorbic acid is
distributed in a vegetal-animal gradient. At the blastula stage, when the
first gradient of reduction in an animal-vegetal direction is formed, the
ascorbic acid seems regularly distributed. At this stage no connection
appears to exist between ascorbic acid distribution and the animalvegetal reduction gradient.
The SH-containing substances constitute another group of reducing
substances. They have been studied by Bäckström (1958b, 1959a) by
histochemical and biochemical methods. —SH groups have been determined in the protein fractions and the soluble non-protein fractions.
The non-protein fraction seems essentially made up of glutathione.
During the cleavage and gastrula stages the content of —SH groups
shows cyclical changes. In embryos treated by lithium, as well as in
embryos animalized by iodosobenzoic acid, the —SH content is lower
than that in the controls. At hatching the normal, animalized or
vegetalized larvae have the same —SH content. After hatching the —SH
content decreases in the three types of larva. The decrease is faster in
the vegetalized larva, and slower in the animalized larva than in the